| 摘要 |
PURPOSE:To prevent a lag in working of a variable-capacity hydraulic pump by controlling a pilot pressure signal led to a pressure receiving portion of a servo- valve according to pressure of each main circuit on discharge side and suction side in a control unit for a hydraulic shovel. CONSTITUTION:A pilot pressure signal is output from a pilot valve 11A by operation of an operation lever 10A. If each pressure of main circuits A, B is zero, a first control valve 15 is located at a neutral position 15C, so that the pilot pressure signal is led to a first pressure receiving portion 6a of a servo- valve 6 so as to switch the servo-valve 6 over to a switching position 6A. Control oil from a control hydraulic source 9 passes through the valve 6 into a left oil chamber 5A of a controlling actuator 5 so as to move a piston to the right, which causes a squeezing capacity changing mechanism 4 to move from a neutral position in such a manner as to discharge toward the main circuit A, so that a variable-capacity hydraulic pump 1 discharges pressure oil to the main circuit A. |
